I'm in the process of designing and building cabinets for a JBL system using Pi 800 Hz crossovers: 2235H woofer, 2445H mid-high, 2380A horn and (eventually) 2405H crossed over at perhaps 8 kHz.

First, I'd be grateful to learn of any JBL model that used the 2235 LF driver: being a technical ignoramus I'd prefer, for cabinet and port dimensions as well as for the drivers' positions on the baffle, to copy a JBL design, as they are much more likely to have "got it right" than I could ever hope to.

I can't seem to find anything on the Lansing Heritage website, but perhaps I've just missed it. . .

Second, this may be a really dumb question, but it seems to me that the 30+ lbs. 2445 compression driver really needs to be supported at least using the "structural foam" 2380 biradial horn. For mounting the driver/horn inside the cabinet, I am assuming one would have to have the 2445 resting on, or bluetacked to, something like a brace. Am I on the right track here?

Many thanks,

Joel Tatelman.

The 2235 works very well in vented cabinets of 2.5ft3 to 10.0ft3, tuned between 20Hz and 30Hz. For a wide range operation, I'd prefer them in 2.5ft3 to 4.0ft3 tuned to 30Hz. For deeper operation, put them in larger 4.0ft3 to 8.0ft3 cabinets and tune them for 25Hz. And for subs, you can max out the box size at 10 or even 12 cubic feet for an EBS alignment tuned to 20Hz.

About bracing, you know that you can't really brace something like this too much. There are some situations where stiffening something or holding it more firmly can cause other problems, but this isn't one of them. As long as your braces don't make it difficult to service, I say put 'em in.

I'm glad that you picked up those 2380 horns that we talked about over the email. They really are a lot better suited to your application than the 2382's.

If your using the Pi Crossover (which I initially suggested), then that'll augment the high frequencies and makes a UHF tweeter not required. You can use a UHF tweeter if you leave out the compensation circuit on the compression driver, but I'd rather not do it this way. Crossover points this high shifts crossover nulls closer towards the on axis position, and the extra crossover point itself introduces further means for nulls, especially when its this high. I think in a setup like yours, a UHF tweeter just isn't needed for good performance.

I'm not sure of which JBL models use the 2235 in particular, but you shouldn't be worried about its performance. Like Wayne said, it's a great driver. As for copying baffle spacing/port dimensions etc - there isn't any need for that. I made a couple of suggestions for the 2235 woofer in one of my emails to you a while ago, and also some reccomended port sizes for both low and high power applications. You'll get all the help you need regarding the rest of the setup - baffle spacing, crossovers, etc from people on this forum, and with the parts your using, you'll definitly end up with a very nice sounding system.

I'd probably use a brace for a heavy compression driver too. It should hold itself up, but the 'mere thought of snaping or damaging the horn flare, especially when moving the cabinet around, is horrifying. I've used a brace for the compression driver to rest on in my 3-way towers to avoid damage to the horn flare.

Adrian

For heavy drivers like the 2445, I use a panel running full width of cabinet, with a round hole same diameter as rubber surround on driver. when the horn is mounted, the driver is a snug fit in the hole. You can see this in the 12" design on my horns page.

Cheers

• My horns page

http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4430LR.pdf
http://www.jblpro.com/pub/technote/tn_v3n01.pdf
http://www.jblpro.com/pub/technote/tn_v3n03.pdf
http://www.jblpro.com/pub/obsolete/443035.pdf
http://www.jblpro.com/pages/components/2235h.htm

Have fun!

Dan

For me, copying the 4430 cabinet is probably the way to go.

Otherwise, I shall have to choose between, now, five different recommendations for box volume and port tuning--all from knowledgeable people (Wayne and Adrian among them), and all, as your comments show, very suitable for the drivers.

One related thing I've been wondering about is achieving a smaller footprint by making the cabinet taller, but narrower and shallower, for example changing a 31" H x 24" W x 23" D cabinet (approx. dimensions of the JBL 4333A) to, say, 36" x 20" x 21". Does one need to worry about skewing proportions?

For some reason my computer is using QuickTime to read PDFs, and is only reproducing the first page of each, so I'll probably have to wait until Monday at the office to see what information JBL gives about the 4430.

Thanks again, guys!

Regards,

Joel.

http://www.lansingheritage.org/html/jbl/specs/pro-speakers/1984-4430-35.htm

The 4430 uses the 2344 horn so it's impossible to copy JBL's design on this one.

No problem in changing cabinet dimensions so long as internal volume is kept the same. There are changes - a larger baffle means that the frequency where it behaves as though its in half space condition is lowered, and vice versa; smaller baffles raise the frequency where the baffle forms a half space condition. Sound becomes more constrained with a larger baffle, i.e: increased directionality. Changes of baffle dimensions and shape also affects the severity of cabinet diffraction.

About the changes you want to do however - from 31*24*23" to 36*20*21", is a small enough change that you don't need to worry about anything.

Adrian

Thanks for clarifyng the cabinet dimensions issue. Now that I've managed to download the pdf of the 4430 studio monitor, I can see that changing dimensions will be less of an issue than I thought. The 4430 is 35.75" H x 21.875" W x 15.75" deep, almost identical dimensions to my Tannoy DMT 15 II monitors. I may have to make the cabs a bit taller to fit everything on the front baffle (ports, woofer, 2380A horn), but haven't done exactly measurements yet. Another option, suggested by one friend, is to mount the horn on top of, not inside the cabinet. This will make vertically aligning the driver voice coils simple. Decisions, decisions. . .

As you pointed out, thte 4430 cabinet is a adequate model for a bass cabinet, but with the different HF driver and horn that I'm using, no more than that.

Will try to work out complete cabinet plans next week. . .

Best regards,

Joel.

> Another option, suggested by one friend, is to mount the horn on
> top of, not inside the cabinet. This will make vertically
> aligning the driver voice coils simple.

True, but at the same time, that will introduce diffraction as well. Horn tweeters usually are a little longer than the woofer, so pushing the tweeter forward to align the acoustic centers will introduce more severe diffraction around the edges of the mouth as it transitions not to the baffle, but rather to open air.

In any case, having some upward axis tilt will optimize the listening position for both on-axis and also above axis positions as well (such as when your standing up) by shifting the nullaxis further up.

> you pointed out, thte 4430 cabinet is a adequate model for a bass
> cabinet, but with the different HF driver and horn that I'm using,
> no more than that.

Thats true. Keep in mind though, some changes of HF horn will change things a lot, particularly the crossover network. In any case - your 2380 is suitable for the application, and you've also got the π crossover which is suitable for the 2445/2380 combination. Your speaker will just have a little different specifications from the original 4430, but that isn't a concern anyway.

In case your interested - there's an AES article which covers design aspects and such of JBL's 4430 and 4435 studio monitors. You can either get it off JBL, or download it from the Pi Speakers website, linked below;

Download AES paper Improvements in Monitor Loudspeaker Systems

The same sort of design principles discussed in that paper are implemented in the Pi Speakers systems, and that's the same sort of design we've all been directing you to. So you wouldn't have lost any performance in your design anyway, even if you had never seen the 4430 datasheet.

Adrian